A search will be conducted for new classes of conditional mutants of yeast deficient in the synthesis and regulation of important membrane lipids. These new classes of mutants together with existing fatty acid and inositol mutants will be used to study the dependence of basic cellular processes such as macromolecular synthesis, cell division and nuclear division on lipid biosynthesis. The mutants will also be used in studies of the role of specific lipids in membrane assembly. Since lipids are important components of biomembranes, it is hoped that the information gained will give insight into the timing and control of membrane biosynthesis during cell division and into the structural and functional role of individual lipids in membranes. Because membranes are involved in a multiplicity of cellular processes including transport of substances into and out of cells, they necessarily play an important role in both normal and abnormal cell growth and differentiation. The information gained from the study of membrane components in a model eukaryote such as yeast may, therefore, be expected to contribute to an understanding of the role of membranes in these processes.